1. Field of the Invention
This document relates to a backlight unit capable of reducing heat and noise and a liquid crystal display (LCD) using the same.
2. Discussion of the Related Art
A liquid crystal display (LCD) has the characteristics of being light and thin and driven with low power consumption, so its applications are growing. The LCD is employed for a mobile computer such as a notebook computer, office automation equipment, audio/video devices, indoor/outdoor advertisement display device, and the like. A transmission type LCD, which is the most common LCD, displays an image by modulating light incident from a backlight unit by controlling an electric field applied to a liquid crystal layer.
The backlight unit is classified into a direct type backlight unit and an edge type backlight unit. The direct type backlight unit has such a structure that several light sources are arranged in a row on a lower surface of a light guide plate to allow light to directly proceed to a front surface of an LCD. The edge type backlight unit has such a structure that light sources are disposed to face the side of a light guide plate and a plurality of optical sheets are disposed between a liquid crystal panel and the light guide plate. In the edge type backlight unit, when the light sources irradiate light to one side of the light guide plate, the light guide plate converts linear light or point light outputted from the light sources into planar light and makes the planar light proceed to a front surface an LCD.
Conventionally, lamp-type light sources, such as CCFL (Cold Cathode Fluorescent Lamp), HCFL (Hot Cathode Fluorescent Lamp), EEFL (External Electrode Fluorescent Lamp), and the like, have been in use as light sources of the backlight unit. Recently, a light emitting diode (LED), which has advantages of being driven at a low voltage to reduce power consumption, having excellent color reproduction (or a color gamut) and contrast ratio, and having a long life span, is drawing attention, but it has problems with a heat generation and a light efficiency as low as one-third of that of lamp-type light sources. Thus, the lamp type light sources are still favored and commonly used.
A backlight unit employing lamp type light sources comprise an inverter applying driving power to drive the lamps. The inverter comprises a controller, a driver, a transformer, and a detector. The controller generates a driving frequency according to DC power supplied from a power supply source. The driver generates an AC current in response to the driving frequency generated from the controller. The transformer receives the AC current which has been generated by the driver, boosts (or raises) its voltage, and supplies the same to the lamps to turn on the lamps to illuminate light. The detector detects current from a resistor and transfers a signal including a state of the lamps to the controller as a feedback, so that the controller can control the inverter entirely.
The related art LCD having such an inverter will now be described. With reference to FIGS. 1 and 2, the related art LCD comprises a liquid crystal panel 50 for displaying an image, a top case 60 for protecting the liquid crystal panel, a plurality of lamps 10 disposed at predetermined intervals in a row and generating light, power terminal units 11 to which both ends of the lamps 10 are fastened, a reflective plate 12 for reflecting light, which goes toward a lower side of the lamps, toward an upper side of the lamps 10, a cover bottom 15 disposed under the reflective plate 12 to protect the lamps 10, the power terminal units 11 and the like, an inverter 20 disposed under the cover bottom 15, supplying driving power to the lamps 10, and comprising an inverter circuit unit 18 having a controller, a driver, and a detector, and a transformer 19, and an inverter cover shield 22 provided under the transformer 19 and protecting the inverter circuit unit 18 and the transformer 19. As shown in FIG. 2, the cover bottom 15 comprising a transformer cover shield comprises a data driving circuit cover shield 23 for protecting a data driving circuit (not shown) and a gate driving circuit cover shield 25 for protecting a gate driving circuit (not shown).
However, the inverter comprises a switching element such as a metal oxide semiconductor field effect transistor (MOSFET) in the driver in order to convert a DC voltage and a DC current into an AC voltage and an AC current and a transformer for boosting the AC voltage which has been converted into the AC current in the driver. According to the above-mentioned construction there are some problems that heat is generated by the MOSFET and vibration is generated by the transformer, thereby shortening a lift span of the device.